Projection optical system and head-up display device

ABSTRACT

An object of the present invention is to provide a compact head-up display device. The head-up display device of the present invention includes an image forming unit that emits image light containing image information, and an eyepiece optical system that displays a virtual image by reflecting the image light, in which the eyepiece optical system includes a concave lens, a free curved surface lens, and a free curved surface concave mirror disposed in order from the image forming unit side along the emission direction of the image light.

TECHNICAL FIELD

The present invention relates to a projection optical system and ahead-up display device.

BACKGROUND ART

There is known a head-up display device in which an image is projectedto a windshield provided in a mobile object such as an automobile and anairplane, and the projected image is observed as a virtual image throughthe windshield.

In Patent Literature 1 for example, as a head-up display deviceaccording to a prior art, there is disclosed a device “provided with aprojection optical system in which light is irradiated from the back ofa transmission type liquid crystal display panel, and an image displayedon the liquid crystal display panel is enlarged and projected(excerption of the abstract)”.

Also, in In Patent Literature 2, there is disclosed “A display apparatusthat includes a first mirror and a second mirror in order along anoptical path from a display device to a viewer (to guide the image to aviewpoint area of the viewer and to display a virtual image), andsatisfies conditions of θx>θy (θx: an incident angle in the long axisdirection of the image on the first mirror, θy: an incident angle in theshort axis direction of the image on the first mirror) and 0.2<D1/Lh<0.9(D1: a distance between an image display surface of the display deviceand the first mirror (an optical path length at the center of theviewpoint area, Lh: a horizontal width of a virtual image visuallyrecognized by the viewer) (excerption of the abstract)”.

Also, in Patent Literature 3, there is disclosed a display device foruse in a vehicle including “a correction member that is disposed betweena windshield and a display device and transmits light of an image therethrough so as to correct the image to be projected on the windshield sothat distortion of the image, which is seen from an eye point, arisingfrom non-plane of a projection area is canceled out (excerption of theabstract)”.

Further, in Non-patent Literature 1, there is disclosed a head-updisplay device that includes tilting of a screen and a configuration ofdisposing a convex lens as a field lens in order to correct distortionarising in a concave mirror.

CITATION LIST Patent Literature

PATENT LITERATURE 1: JP-A No. 2009-229552

PATENT LITERATURE 2: US Patent Application Publication No. 2016/195719

PATENT LITERATURE 3: US Patent Application Publication No. 2002/084950

Non-Patent Literature

NON-PATENT LITERATURE 1: PIONEER R&D (Vol. 22, 2013)

SUMMARY OF INVENTION Technical Problem

In the head-up display device disclosed in Patent Literature 2, there isprovided a thin type head-up display device that is achieved byarranging a display device and a first mirror (rotationally asymmetricmirror) so as to be shifted in the horizontal direction. However, thefirst embodiment of Patent Literature 2 has the virtual image size of140×70 mm which is horizontally long, and has a configuration of foldingthe light flux in the horizontal direction that has the light flux sizeof 2 times of that of the vertical direction. Therefore, the reflectingmirror becomes large, and compactization of the volume of the head-updisplay device is hard even in the thin type head-up display device.

In an example of the head-up display device disclosed in PatentLiterature 3, although correction of distortion arising from non-planeof the projection area of the windshield is disclosed, consideration isnot given to distortion arising from the concave mirror disclosed inNon-patent Literature 1. With respect to the Non-patent Literature 1also, although the screen is tilted and the convex lens as a field lensis disposed in order to correct the distortion arising in the concavemirror, the performance on the telecentric property in the liquidcrystal display panel disclosed in Patent Literature 1 is not satisfied.Thus, the fact of the projection optical system and the head-up displaydevice is that there is still a room for further improvement forcompactization of the device while securing required performance.

The present invention has been achieved in view of the fact describedabove, and its object is to minimize the optical configuration of aprojection optical system while securing required performance and toprovide a head-up display device of a compact type.

Solution to Problem

In order to solve the problem described above, the present invention hasconfigurations described in claims. As an aspect of the presentinvention, the present invention is a projection optical systemincluding an eyepiece optical system that generates image informationand displays a virtual image by reflecting image light emitted from animage forming unit that emits the image light containing the imageinformation, in which the eyepiece optical system includes a concavelens, a free curved surface lens, and a free curved surface concavemirror disposed in order from the image forming unit side along theemission direction of the image light.

Advantageous Effect of Invention

According to the present invention, it is possible to minimize theoptical configuration of a projection optical system while securingrequired performance and to provide a head-up display device of acompact type. Also, problems, configurations, and effects other thanthose described above will be clarified by explanation of embodimentsdescribed below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a total ray diagram of an eyepiece optical system of thefirst embodiment (YZ plane).

FIG. 1B is a total ray diagram of the eyepiece optical system of thefirst embodiment (XZ plane).

FIG. 2 is an enlarged view of an essential part of the eyepiece opticalsystem of the first embodiment.

FIG. 3 is a drawing that shows lens data of a head-up display deviceaccording to the first embodiment.

FIG. 4 is a drawing of free curved surface factors of the head-updisplay device according to the first embodiment.

FIG. 5A is a drawing that shows the distortion property as viewed fromthe center of an eye box in the first embodiment.

FIG. 5B is a drawing that shows the distortion property as viewed fromthe top right of the eye box in the first embodiment.

FIG. 5C is a drawing that shows the distortion property as viewed fromthe top left of the eye box in the first embodiment.

FIG. 5D is a drawing that shows the distortion property as viewed fromthe bottom left of the eye box in the first embodiment.

FIG. 5E is a drawing that shows the distortion property as viewed fromthe bottom right of the eye box in the first embodiment.

FIG. 6 is a spot diagram on a liquid crystal display panel when anobject point is disposed on a virtual image plane.

FIG. 7A is an angle shift diagram of a main ray Ray 1 and an imaginalray Ray 0 at each field angle position.

FIG. 7B is a drawing that shows the angle θ between the main ray Ray 1and the imaginal ray Ray 0.

FIG. 8A is a total ray diagram of an eyepiece optical system of thesecond embodiment (YZ plane).

FIG. 8B is a total ray diagram of the eyepiece optical system of thesecond embodiment (XZ plane).

FIG. 9 is an enlarged view of an essential part of the eyepiece opticalsystem of the second embodiment.

FIG. 10 is a drawing that shows lens data of a head-up display deviceaccording to the second embodiment.

FIG. 11 is a drawing of free curved surface factors of the head-updisplay device according to the second embodiment.

FIG. 12A is a drawing that shows the distortion property as viewed fromthe center of an eye box in the second embodiment.

FIG. 12B is a drawing that shows the distortion property as viewed fromthe top right of the eye box in the second embodiment.

FIG. 12C is a drawing that shows the distortion property as viewed fromthe top left of the eye box in the second embodiment.

FIG. 12D is a drawing that shows the distortion property as viewed fromthe bottom left of the eye box in the second embodiment.

FIG. 12E is a drawing that shows the distortion property as viewed fromthe bottom right of the eye box in the second embodiment.

FIG. 13 is a spot diagram of a head-up display device of the secondembodiment.

FIG. 14A is an angle shift diagram of a main ray and the normal line ofa liquid crystal display panel at each field angle position.

FIG. 14B is a drawing that shows the angle θ between the main ray andthe normal line of the liquid crystal display panel.

FIG. 15A is a ray diagram obtained by projecting a ray from a windshieldto a focus position of the light flux (exit pupil position) to the YZcross section.

FIG. 15B is a ray diagram obtained by projecting a ray from a freecurved surface concave mirror to the focus position of the light flux(exit pupil position) to the XZ cross section.

FIG. 16A is a ray tracking diagram of a case where a diaphragm isdisposed to be apart from a convex lens by equal to or greater than afocal point distance of a convex lens (equivalent to the free curvedsurface concave mirror).

FIG. 16B is a ray tracking diagram that displays up to a position beyondthe image plane in order to display the focus position.

FIG. 16C is a ray tracking diagram of a case of using a basicconfiguration for correcting the telecentric property and thedistortion.

FIG. 17 is a schematic configuration drawing of a head-up displaydevice.

FIG. 18 is a schematic configuration drawing of an image forming unitprovided in a head-up display device according to the third embodiment.

FIG. 19 is a schematic configuration drawing of an image forming unitprovided in a head-up display device according to the fourth embodiment.

FIG. 20 is a functional block diagram of the image forming unit.

FIG. 21 is a plan view of an automobile that is a movable object asviewed from the front.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment and various examples of the present inventionwill be explained using the drawings and the like. Explanations belowshow concrete examples of the content of the present invention, thepresent invention is not limited to these explanations, and variousalterations and amendments by a person with an ordinary skill in the artcan be effected within the range of the technical thoughts disclosed inthe present description. Also, in all drawings for explaining thepresent invention, those having a same function are marked with a samereference sign, and there is a case of omitting repeated explanation forthem. Hereinafter, items common to all embodiments will be explained,and the features of each embodiment will be explained next.

The basic configuration of a head-up display device 30 will be explainedusing FIG. 17. FIG. 17 is a schematic configuration drawing of thehead-up display device 30.

The head-up display device 30 shown in FIG. 17 has such configurationthat image light emitted from a projection optical system 20 includingan image forming unit 10 and an eyepiece optical system 5 is made to bereflected by a windshield 6 of an automobile and is made to be incidenton eyes 9 of a viewer. By this configuration, as viewed from the eyes 9of the viewer, it becomes a state where as if image information isviewed at a virtual image plane 7. The direction along which the imagelight emitted by the image forming unit 10 is reflected by thewindshield 6 after passing through the eyepiece optical system 5 isequivalent to the emission direction of the image light.

First, the image forming unit 10 will be explained referring to FIG. 20.FIG. 20 is a functional block diagram of the image forming unit. Asshown in FIG. 20, the image forming unit 10 includes a liquid crystaldisplay panel 2, a backlight 1, and a controller 200 that controlsoperation of them. The image forming unit 10 irradiates light from thebacklight 1 to the liquid crystal display panel 2, and emits imageinformation (image information) displayed on the liquid crystal displaypanel 2 toward the eyepiece optical system 5.

The controller 200 includes a control device 201. To this control device201, various information is inputted from external devices. For example,as the external devices, a navigation system 208 and an ECU (ElectronicControl Unit) 209 are connected to the control device 201, thenavigation system 208 being a navigation apparatus that generates andoutputs information on the motion of a movable object mounted with thehead-up display device 30, the ECU 209 controlling the motion of themovable object. Various kinds of sensors 210 included in the movableobject are connected to the ECU 209, and it is configured to notify theECU 209 of detected information.

The controller 200 includes the control device 201 and a backlight drivecircuit 207, the control device 201 processing various kinds of datafrom the external devices explained above, the backlight drive circuit207 being for driving the backlight 1.

The control device 201 includes a microcomputer 202 and a storage device206 that is connected to the microcomputer 202.

The microcomputer 202 includes a RAM (Random Access Memory) 203, a CPU(Central Processing Unit) 205, and a ROM (Read Only Memory) 204, the RAM203 being for storing various kinds of data from the external devices,the CPU 205 for executing a calculation process for generating imagedata that become a source of a virtual image viewed by the viewer, theROM 204 storing a program and a parameter which can execute thecalculation process in the CPU 205.

The controller 200 having the configuration described above displaysimage information on the liquid crystal display panel 2 that is includedin the image forming unit 10. The image forming unit 10 emits the imageinformation displayed on the liquid crystal display panel 2 as an imagelight flux by a light flux irradiated by the backlight 1.

Returning to FIG. 17, the image light flux generated and emitted in theimage forming unit 10 is projected to the windshield 6 by the eyepieceoptical system 5. The image light flux projected to the windshield 6 isreflected by the windshield 6, and reaches the position of the eyes 9 ofthe viewer. Thus, as viewed from the eyes 9 of the viewer, such relationas if the image information of the virtual image plane 7 is viewed isestablished.

As shown in FIG. 17, imaginal points of a point Q1, a point Q2, and apoint Q3 are assumed at the emission plane of the image light flux atthe liquid crystal display panel 2. When imaginal points at the virtualimage plane 7 to which the image light flux emitted from these imaginalpoints correspond are considered, a point V1, a point V2, and a point V3correspond to them as shown in FIG. 17. A range where the point V1, thepoint V2, and the point V3 at the virtual image plane 7 can be viewedeven when the viewer moves the position of the eyes 9 is an eye box 8.

Although FIG. 17 illustrates the head-up display device 30 by a sideview, because the actual configuration of the head-up display device 30is cubical, the eye box 8 has a 2-dimensional spread. Thus, the eyepieceoptical system 5 is an optical system that displays an image (virtualimage) of an object (spatial image) in front of the eyes of a viewersimilarly to an ocular lens of a finder of a camera or an ocular lens ofa microscope.

Here, an example of a case of mounting the head-up display device 30according to the present embodiment on a movable object will beexplained using FIG. 21. FIG. 21 is a plan view of an automobile 500that is a movable object as viewed from the front. In such automobile500 as shown in FIG. 21, the windshield 6 that is a front glass isdisposed in front of the driver seat as a wind guard.

The head-up display device 30 allows the viewer sitting on the driverseat to be in a state of capable of viewing various kinds of informationrelated to the motion of the automobile 500 as a virtual image byprojecting the image light flux to the windshield 6. The position wherethe image light flux is projected is the front of the driver seat andits surroundings. The image light flux is projected to such position asshown in a rectangular region R1 shown by a dotted line for example.

The condition of the pupil position required for the eyepiece opticalsystem 5 of the head-up display device 30 will be explained using FIG.15 and FIG. 16.

FIG. 15 is a ray diagram that displays the eyepiece optical system 5 bya reduced optical system of a case of being configured of the windshield6 and a free curved surface concave mirror 54 (the free curved surfaceconcave mirror is equivalent to a convex lens) which are a requisiteminimum configuration. Although the liquid crystal display panel 2 isdisposed within the head-up display device 30 in fact as shown in FIG.20, each drawing of FIG. 15A and FIG. 15B illustrates a state of a rayof only the main ray in a state of omitting illustration of the liquidcrystal display panel for facilitating explanation of an exit pupilposition 101 in the reduced optical system where the virtual image planeside is made an object, making the pupil diameter 0.001 mm, and beingconfigured of only the windshield 6 and the free curved surface concavemirror 54.

The coordination system of FIG. 15A and FIG. 15B is defined that thehorizontal direction of the eye box 8 is X-axis, the vertical directionis Y-axis, and the direction perpendicular to XY-plane is Z-axis.

FIG. 15A is a ray diagram obtained by projecting a ray from thewindshield 6 to the focus position 101 (exit pupil position) of thelight flux to the YZ cross section, and FIG. 15B is a ray diagramobtained by projecting a ray from the free curved surface concave mirror54 to the focus position 101 (exit pupil position) of the light flux tothe XZ cross section.

In order to make the head-up display device 30 compact, it is preferableto dispose the liquid crystal display panel at a position nearestpossible to the free curved surface concave mirror 54 in the positionavoiding the optical path from the windshield 6 to the free curvedsurface concave mirror 54. Therefore, in the reduced optical systemwhere the virtual image plane of FIG. 15A and FIG. 15B is made anobject, the exit pupil of the eyepiece optical system 5 comes to bepositioned at a location after passing through the liquid crystaldisplay panel.

In the meantime, in the ordinary combination of the liquid crystaldisplay panel 2 and the backlight 1, the incident/emitting side of theliquid crystal display panel is made telecentric.

Here, in order to satisfy this telecentric property (the exit pupildistance is infinitely great) on the liquid crystal display panel sideof FIG. 15A and FIG. 15B, it is required to dispose a concave lenshaving a negative refraction power immediately before the liquid crystaldisplay panel as a field lens.

The action of this field lens and the action of the free curved surfacelens will be explained using FIG. 16A to FIG. 16C. FIG. 16A is a raytracking diagram of a case where a diaphragm is disposed to be apartfrom a convex lens by equal to or greater than a focal point distance ofthe convex lens (equivalent to a free curved surface concave mirror). Adiaphragm 102 is disposed to be apart from a convex lens 103 by equal toor greater than the focal point distance of the convex lens 103(equivalent to the free curved surface concave mirror 54), the main raythat passes through the center of the diaphragm 102 receives a largerefraction power at the convex lens 103, and the main ray converges andis made incident to an image plane 104. At the same time, because theray height H of the actual ray becomes lower than the height H₀ of theparaxial ray at the image plane 104 because of the aberration occurringat the convex lens 103, distortion of a barrel shape occurs at the imageplane 104.

FIG. 16B is a ray tracking diagram that displays up to a position beyondthe image plane 104 in order to display the focus position 101, and itcan be confirmed that the telecentric property has deteriorated.

FIG. 16C is a ray tracking diagram of a case of using a basicconfiguration for correcting the telecentric property and thedistortion. Improvement of mainly the telecentric property is achievedby disposing a concave lens 51 immediately before the image plane 104,the concave lens 51 having a focal point distance that is equivalent tothe distance between the image plane 104 and the focus position 101 ofFIG. 16B, and mainly the distortion is corrected by bringing the rayheight H of the actual ray at the image plane 104 close to the rayheight H₀ of the paraxial ray by a free curved surface lens 52 that isdisposed before the concave lens 51.

Here, although it is possible to omit the concave lens 51 by providingthe free curved surface lens 52 itself with a negative refraction power,the surface inclination of the lens surface of the free curved surfacelens 52 becomes large. Therefore, by separation into the free curvedsurface lens 52 and the concave lens 51, productivity of the free curvedsurface lens 52 improves, and difference of the position of the freecurved surface lens 52 and the position of the concave lens 51, namelydifference in the ray height, namely the degree of freedom is effectivein correction of the telecentric property and the distortion.

Although detailed definition expression will be explained below, becausethe definition expression of the free curved surface lens 52 includes anXY polynomial expression, it is possible to provide a horizontallyasymmetric and vertically asymmetric lens action, and it is alsoeffective for correction of horizontally asymmetric and verticallyasymmetric distortion property occurring in the windshield 6.

Also, it is preferable to dispose the concave lens 51 so as to opposethe light irradiation surface of the liquid crystal display panel 2(refer to FIG. 20) and to minimize the distance to the light irradiationsurface (contacts the light irradiation surface when the distance is 0).Therefore, in the concave lens 51, the surface opposing the lightirradiation surface of the liquid crystal display panel (will behereinafter referred to as an “opposing surface”) is formed into a flatshape. Thus, it becomes easy to dispose the entire surface of theopposing surface closer to the liquid crystal display panel compared toa case where the opposing surface of the concave lens 51 is formed intoa concave surface. At that time, by attaching the concave lens 51 to theliquid crystal display panel 2 through a holding member 25 (refer toFIG. 9), it becomes easy to dispose the concave lens 51 more closer tothe liquid crystal display panel 2.

Also, when the opposing surface of the concave lens 51 is formed into aconcave surface, because the end part of the concave surface becomescloser to the liquid crystal display panel 2 compared to the center partof the concave surface, the necessity of disposing the concave lens 51itself to be apart from the liquid crystal display panel 2 occurs.Further, because the range where the pixels can be displayed in theliquid crystal display panel 2 is larger than the effective size of theimage light in the liquid crystal display panel 2 and structures existoutside the range also, disposal of the concave lens 51 to be apart fromthe liquid crystal display panel 2 becomes increasingly necessary inorder to avoid structural interference with the concave lens 51 takingthe structures into consideration. Based on the fact, it is assumed thatthe opposing surface with the liquid crystal display panel 2 in theconcave lens 51 is formed preferably into a flat surface instead of aconcave surface.

Also, it is preferable that the concave lens 51 has such opticalproperty satisfying a condition that a value obtained by dividing thefocal point distance of the concave lens 51 by the focal point distanceof the free curved surface concave mirror 54 is equal to or greater than−0.6 and equal to or smaller than −0.3.

The meaning of the condition will be explained using FIG. 15 thatdisplays ray tracking in the reduced optical system. When the refractionpower of the free curved surface concave mirror 54 (=inverse number ofthe focal point distance) is strong, the focus position of the lightflux reflected by the free curved surface concave mirror 54 becomesclose to the free curved surface concave mirror 54. To the contrary,when the refraction power of the free curved surface concave mirror 54is weak, the focus position of the light flux reflected by the freecurved surface concave mirror 54 becomes apart from the free curvedsurface concave mirror 54. Also, with respect to the concave lens 51 forachieving a telecentric state of the light flux, when the refractionpower of the free curved surface concave mirror 54 is strong, it isrequired to strengthen the refraction power (a negative value) of theconcave lens 51 also. To the contrary, when the refraction power of thefree curved surface concave mirror 54 is weak, it is required to weakenthe refraction power of the concave lens 51 also. Accordingly, the mainray at the liquid crystal display panel 2 becomes a converged state whenthe ratio of the focal point distance is less than −0.6, and the mainray at the liquid crystal display panel 2 becomes a diverged state whenthe ratio of the focal point distance is larger than −0.3.

Also, the inverse number of the focal point distance is the refractionpower, a strong refraction power means that the absolute value of theinverse number is large, and, to the contrary, a weak refraction powermeans that the absolute value of the inverse number is small.

Next, the first embodiment of the projection optical system using thefree curved surface concave mirror 54, the free curved surface lens 52,and the concave lens 51 capable of achieving the head-up display device30 of a compact type will be explained.

First Embodiment

The first embodiment has a feature in the configuration of the eyepieceoptical system 5 out of the head-up display device 30 of FIG. 17. Thewindshield 6 and the eyepiece optical system 5 configuring theprojection optical system will be explained referring to FIG. 1. FIG. 1Ais a total ray diagram of the eyepiece optical system 5 of the firstembodiment, and shows a situation of viewing image information of thevirtual image plane 7 with the eyes of the viewer in YZ plane defined bythe horizontal direction X-axis of the eye box 8, the vertical directionY-axis, and Z-axis perpendicular to XY-axis. Also, FIG. 1B is a totalray diagram of the eyepiece optical system 5 of the first embodiment,and shows a situation of viewing the image information of the virtualimage plane 7 with the eyes of the viewer in XZ plane.

The right eye and the left eye overlap in YZ plane (refer to thereference sign 9 of FIG. 1A), and the right eye and the left eye areseen separately in XZ plane (refer to the reference sign 9 of FIG. 1B).As shown in FIG. 1A, the virtual image plane 7 is disposed so as to betilted with respect to the field of view direction. To be more specific,the virtual image distance is increased on the upper side of the fieldof view (the positive side of Y-coordinate), and the virtual imagedistance is reduced on the lower side of the field of view (the negativeside of Y-coordinate). Since the windshield 6 has a symmetric shape withrespect to the right-left direction of an automobile, the range of thewindshield 6 where the effective light flux passes through in thehead-up display device 30 is displayed symmetrically in the right-leftdirection.

FIG. 2 is an enlarged view of an essential part of the eyepiece opticalsystem of the first embodiment. As shown in FIG. 2, the eyepiece opticalsystem 5 is configured by disposing the concave lens 51, the free curvedsurface lens 52, a reflecting mirror 53, the free curved surface concavemirror 54 having a positive refraction power, and the windshield 6 whichare arrayed in order from a polarization plate 21 (a component of theliquid crystal display panel 2) side. The concave lens 51 is disposed tooppose an emission surface 22 of the image light of the liquid crystaldisplay panel 2. The refraction power of the eyepiece optical system 5is mainly borne by the free curved surface concave mirror 54.Telecentric property is achieved mainly by the concave lens 51, anddistortion is corrected mainly by the free curved surface lens 52. It isknown that compactization of the head-up display device 30 has beenachieved by that the reflecting mirror 53 is positioned below an opticalpath along which a light flux reflected by the windshield 6 is headed tothe free curved surface concave mirror 54, and by that the free curvedsurface lens 52 is positioned below the optical path.

FIG. 3 is a drawing that shows lens data of the head-up display device30 according to the first embodiment. In the lens data shown in FIG. 3,the radius of curvature is expressed by a positive mark when the centerposition of the radius of curvature is positioned in the proceedingdirection, and the interplanar distance expresses the distance on theoptical axis from the apex position of each surface to the apex positionof the next surface.

As shown in FIG. 3, the first interplanar distance d1 (refer to FIG. 9)from the emission surface 22 (equivalent to the surface 12 of FIG. 3) ofthe image light in the liquid crystal display panel 2 to an opposingsurface 51 a (refer to FIG. 9; equivalent to surface 11 of FIG. 3) thatopposes the liquid crystal display panel 2 in the concave lens 51 is0.122, the second interplanar distance d2 (refer to FIG. 9) from theopposing surface to an emission surface 51 b (refer to FIG. 9;equivalent to surface 10 of FIG. 3) where the image light made to beincident to the concave lens 51 is emitted from the concave lens 51 is4.700, and therefore the first interplanar distance d1 is shorter thanthe second interplanar distance d2. That is, the concave lens 51 isdisposed so as to be closer to the liquid crystal display panel 2 thanthe thickness of the concave lens 51. It is preferable that the firstinterplanar distance d1 is as small as possible, namely the concave lens51 is preferable to be located as close as possible to the liquidcrystal display panel 2, and the concave lens 51 comes to be disposed soas to contact the liquid crystal display panel 2 in the case of d1=0.

Decentering is a value of each of X-axis direction/Y-axisdirection/Z-axis direction, and tilting is rotation aroundX-axis/rotation around Y-axis/rotation around Z-axis. With respect todecentering/tilting, decentering and tilting are applied to the surfacein question in order. In “normal decentering”, at the position of theinterplanar distance on a new coordinate system to whichdecentering/tilting has been applied, the next surface is disposed.Decentering and tilting of “decenter & return” are applied only to thesurface in question, and do not affect the next surface. Also, rotationaround X-axis is positive for the clockwise direction as viewed from thepositive direction of X-axis, rotation around Y-axis is positive for theclockwise direction as viewed from the positive direction of Y-axis, androtation around Z-axis is positive for the counterclockwise direction asviewed from the positive direction of Z-axis.

Glass material name 50.30 expresses material having the refraction indexof 1.50 and the Abbe number of 30, and glass material name 52.60expresses material having the refraction index of 1.52 and the Abbenumber of 60.

Surface 2 (the windshield 6) is an anamorphic aspherical surface, andcan be obtained by the formula (1) below using the radius of curvature9,686 mm (=1/cuy) of Y-direction and the radius of curvature 5,531 mm(=1/cux) of X-direction.

$\begin{matrix}{\lbrack {{Formula}\mspace{14mu} 1} \rbrack \mspace{625mu}} & \; \\{Z = \frac{{{cux} \cdot x^{2}} + {{cuy} \cdot y^{2}}}{1 + \sqrt{ {1 - {( {1 + {Kx}} ){{cux}^{2} \cdot x^{2}}} - {( {1 + {Ky}} ){{cuy}^{2} \cdot y^{2}}}} )}}} & (1)\end{matrix}$

FIG. 4 is a drawing of free curved surface factors of the head-updisplay device 30 according to the first embodiment. The free curvedsurface factors of FIG. 4 are obtained by the formula (2) below.

$\begin{matrix}{\lbrack {{Formula}\mspace{14mu} 2} \rbrack \mspace{625mu}} & \; \\{{Z = {\frac{c \cdot ( {x^{2} + y^{2}} )}{1 + \sqrt{1 - {( {1 + K} ){c^{2} \cdot ( {x^{2} + y^{2}} )}}}} + {\sum{\sum( {{{Cj}( {m,n} )} \times x^{m} \times y^{n}}\; )}}}}{{{wherein}\mspace{14mu} j} = {{\lbrack {( {m + n} )^{2} + m + {3n}} \rbrack/2} + 1}}} & (2)\end{matrix}$

The free curved surface factor C_(j) represents a shape that isrotationally asymmetric with respect to each optical axis (Z-axis), andrepresents a shape that is defined by the component of the conic termand the component of the XY polynomial expression term. For example,when X is 2-dimensional (m=2) and Y is 3-dimensional (n=3), the factorof C₁₉ where j=[(2+3)²+2+3×3]/2+1=19 corresponds.

Also, the position of the optical axis of each of the free curvedsurface is determined by the quantity of decentering/tilting in the lensdata of FIG. 3.

Hereinafter, values of the eye box size, the field of view angle, andthe like of the eyepiece optical system of the first embodiment will beshown in order of the horizontal direction and the vertical direction.

Eye box size 130 × 40 mm Effective size of image light in liquid 67.4 ×29.0 mm crystal display panel Field of view angle (all field angle) 10 ×4 degrees Depression angle 0.7 degree Virtual image distance 16.5 m(depression angle direction)

The value obtained by dividing the focal point distance of the concavelens (−143 mm) by the focal point distance of the free curved surfaceconcave mirror (355 mm) is −0.40.

Next, the optical performance of the first embodiment will be explainedusing FIG. 5A to FIG. 5E, FIG. 6, FIG. 7A, and FIG. 7B.

Each drawing of FIG. 5A to FIG. 5E is the drawing that shows thedistortion property of the head-up display device 30 of the firstembodiment. To be more specific, FIG. 5A is a distortion diagram on theliquid crystal display panel 2 side by a ray that passes through thecenter of the eye box 8 with respect to the range of the virtual imageplane 7 having a rectangular shape. FIG. 5B, FIG. 5C, FIG. 5D, and FIG.5E are distortion diagrams on the liquid crystal display panel 2 side bya ray that passes through each point of the top right corner, the topleft corner, the bottom left corner, and the bottom right corner of theeye box 8.

When the eye is positioned at each position within the eye box 8 in astate where a rectangular image is displayed on the liquid crystaldisplay panel 2 side, distortion opposite to that of FIG. 5A to FIG. 5E(example: barrel type↔bobbin type) is observed. Since the distortiondiagrams of FIG. 5A to FIG. 5E have a generally same shape, when animage image matching the distortion diagram of FIG. 5A to FIG. 5E forexample is displayed on the liquid crystal display panel 2, the viewercan observe a rectangular virtual image that has no distortion.

FIG. 6 is a spot diagram of the head-up display device 30 of the firstembodiment. FIG. 6 is a spot diagram on the liquid crystal display panel2 of a case where an object point is disposed on a virtual image plane,and is a drawing that displays a spot diagram by a ray that passesthrough the entire eye box 8 separately by red color (650 nm), greencolor (550 nm), and blue color (450 nm). This spot diagram is a spotdiagram for all light fluxes of the eye box 8 having the size of 130 mmhorizontal×40 mm vertical. In a case of the virtual image viewed by theactual viewer, the spot diagram in the size of the iris of the eye of ahuman body (said to be 7 mm in diameter at a maximum) has been improvedenormously. Here, the spot diagram is a drawing where a spot diagram ateach position of the liquid crystal display panel 2 in the reducedoptical system with the virtual image being made the object surface isenlarged and highlighted by 5 times.

FIG. 7A is an angle shift diagram of the main ray Ray 1 and the imaginalray Ray 0 at each field angle position. Also, FIG. 7B is a drawing thatshows the angle θ between the main ray Ray 1 and the imaginal ray Ray 0.As shown in FIG. 7B, the imaginal ray Ray 0 is a straight line obtainedby rotating the normal line of the liquid crystal display panel 2 by 13degrees around a rotation axis that is parallel to the long side of theliquid crystal display panel 2. That is, it is meant that theillumination optical system is disposed so as to be tilted by 13 degreeswith respect to the liquid crystal display panel 2. From FIG. 7A, it isknown that the maximum value of the angle shift is as less as 1.9degrees.

Therefore, according to the present embodiment, the head-up displaydevice 30 can be provided which is made compact by a projection opticalsystem using a free curved surface concave mirror, a free curved surfacelens, and a concave lens.

Second Embodiment

The second embodiment is featured in that the configuration of theeyepiece optical system 5 is different from that of the firstembodiment. The second embodiment is an embodiment where the liquidcrystal display panel 2 of a compact type is combined, the reflectingmirror 53 is deleted, and priority is given to compactization of thehead-up display device 30.

FIG. 8A is a total ray diagram of the eyepiece optical system 5 of thesecond embodiment, and shows a situation of viewing image information ofthe virtual image plane 7 with the eyes of the viewer in YZ-planedefined by the horizontal direction X-axis, the vertical directionY-axis, and Z-axis perpendicular to XY-axis of the eye box 8. FIG. 8Bshows a situation of viewing the image information of the virtual imageplane 7 with the eyes of the viewer in XZ plane. FIG. 9 is an enlargedview of an essential part of the eyepiece optical system of the secondembodiment.

As shown in FIG. 8A, FIG. 8B, and FIG. 9, in the eyepiece optical system5, the concave lens 51, the free curved surface lens 52, and the freecurved surface concave mirror 54 having a positive refraction power aredisposed in order from a polarization plate 21 (a component of theliquid crystal display panel 2) side, and the windshield 6 is disposedso as to be arrayed next to them.

FIG. 10 is a drawing that shows lens data of the head-up display device30 according to the second embodiment. FIG. 11 is a drawing of freecurved surface factors of the head-up display device 30 according to thesecond embodiment.

Hereinafter, values of the eye box size, the field of view angle, andthe like of the eyepiece optical system of the second embodiment will beshown in order of the horizontal direction and the vertical direction.

Eye box size 130 × 40 mm Effective size of image light in liquid 39.5 ×20.4 mm crystal display panel Virtual image size 240 × 90 mm Field ofview angle (all field angle) 6.9 × 2.6 degrees Depression angle 5.1degrees Virtual image distance 2.1 m

The value obtained by dividing the focal point distance of the concavelens (−90 mm) by the focal point distance of the free curved surfaceconcave mirror (188 mm) is −0.48.

Next, the optical performance of the second embodiment will be explainedusing FIG. 12A to FIG. 12E, FIG. 13, FIG. 14A, and FIG. 14B. FIG. 12A toFIG. 12E are drawings that express the distortion property of thehead-up display device 30 of the second embodiment. To be more specific,FIG. 12A is a distortion diagram on the liquid crystal display panel 2side by a ray that passes through the center of the eye box 8 withrespect to the range of the virtual image plane 7 having a rectangularshape. FIG. 12B, FIG. 12C, FIG. 12D, and FIG. 12E are distortiondiagrams on the liquid crystal display panel 2 side by a ray that passesthrough each point of the top right corner, the top left corner, thebottom left corner, and the bottom right corner of the eye box 8. FIG.13 is a spot diagram of the head-up display device 30 of the secondembodiment. FIG. 14A is an angle shift diagram of a main ray and thenormal line of the liquid crystal display panel 2 at each field angleposition. FIG. 14B is a drawing that shows the angle θ between the mainray and the normal line of the liquid crystal display panel 2. From FIG.14A, it is known that the maximum value of the angle shift between themain ray and the normal line of the liquid crystal display panel 2 is asless as 2.8 degrees.

Therefore, according to the present embodiment, the head-up displaydevice 30 can be provided which is made compact by a projection opticalsystem using a free curved surface concave mirror, a free curved surfacelens, and a concave lens.

Third Embodiment

The third embodiment is featured in that the configuration of the imageforming unit 10 is different from that of the first embodiment and thesecond embodiment. The third embodiment will be explained referring toFIG. 18. FIG. 18 is a schematic configuration drawing of an imageforming unit provided in the head-up display device according to thethird embodiment.

Although image information of the liquid crystal display panel 2 isenlarged directly by the eyepiece optical system 5 and is displayed as avirtual image in the first embodiment, instead of the configuration ofthis image forming unit 10, the liquid crystal display panel 2 that ismore compact is used, image information of the liquid crystal displaypanel 2 is extension-mapped onto a screen plate (diffusion plate) by arelay optical system 3 that generates an image of a light-valve, andimage information of it is enlarged by the eyepiece optical system andis displayed as a virtual image.

To be more specific, the light flux irradiated from the backlight 1 tothe liquid crystal display panel 2 is made to be incident to the relayoptical system 3 as an image light flux including the image informationdisplayed on the liquid crystal display panel 2. The image light isemitted from an emission surface 401 of a screen plate 4 toward theeyepiece optical system 5. By the image forming action in the relayoptical system 3, the image information on the liquid crystal displaypanel 2 is enlarged, and then the image information is magnified andprojected on to the screen plate (diffusion plate) 4. Points P1/P2/P3 onthe liquid crystal display panel 2 correspond to points Q1/Q2/Q3 on thescreen plate (diffusion plate) 4 respectively. By using the relayoptical system 3, a liquid crystal display panel with a small displaysize can be used. Since the backlight 1, the liquid crystal displaypanel 2, the relay optical system 3, and the screen plate (diffusionplate) 4 generate image information (image information) on the screenplate (diffusion plate) 4, they are collectively referred to as theimage forming unit 10.

Also, the screen plate (diffusion plate) 4 is configured of a micro lensarray where micro lenses are disposed 2-dimensionally. Thereby, adiffusion action occurs, the spread angle of the light flux emitted fromthe screen plate 4 is made large, and the size of the eye box 8 is madea predetermined size. Further, the diffusion action of the screen plate(diffusion plate) 4 can be achieved also by incorporating diffusionparticles.

Fourth Embodiment

The fourth embodiment is featured in that the configuration of the imageforming unit 10 is different from that of the first embodiment and thesecond embodiment. The fourth embodiment will be explained referring toFIG. 19. FIG. 19 is a schematic configuration drawing of an imageforming unit provided in the head-up display device according to thefourth embodiment.

Although image information of the liquid crystal display panel 2 ismapped on the screen plate 4 that has a diffusion function in the firstembodiment, instead of the configuration of this image forming unit 10,it may be configured to use a micro electro mechanical system (MEMS)that includes a laser light source 301, and a light scanning section 302that scans laser light emitted from the laser light source 301. Thelight scanning section 302 includes a reflection surface 302 a and areflection surface rotation drive section 302 b. The MEMS generates alight scanning image on the screen plate 4 by light-scanning of thelaser, the screen plate 4 having a diffusion function. The image lightis emitted from the emission surface 401 of the screen plate 4 towardthe eyepiece optical system 5. The image forming unit of the fourthembodiment disposes the position where light scanning is effected byswinging the ray angle by the MEMS according to the exit pupil position.The rotation center position of the MEMS is configured matching aposition assumed on the eyepiece optical system 5 side.

REFERENCE SIGNS LIST

-   1 . . . Backlight-   2 . . . Liquid crystal display panel-   3 . . . Relay optical system-   4 . . . Screen plate (diffusion plate)-   5 . . . Eyepiece optical system-   6 . . . Windshield-   7 . . . Virtual image plane-   8 . . . Eye box-   9 . . . Eyes of driver-   10 . . . Image forming unit-   20 . . . Projection optical system-   30 . . . Head-up display device-   51 . . . Concave lens-   52 . . . Free curved surface lens-   53 . . . Reflecting mirror-   54 . . . Free curved surface concave mirror-   101 . . . Focus position-   102 . . . Diaphragm-   103 . . . Convex lens-   104 . . . Image surface

1. A projection optical system including an eyepiece optical system thatgenerates image information and displays a virtual image by reflectingimage light emitted from an image forming unit that emits the imagelight containing the image information; wherein the eyepiece opticalsystem includes a concave lens, a free curved surface lens, and a freecurved surface concave mirror disposed in order from the image formingunit side along an emission direction of the image light.
 2. Theprojection optical system according to claim 1; wherein an opposingsurface opposing the image forming unit in the concave lens is formedinto a flat shape, and the concave lens is disposed so that an opticalaxis of the concave lens is parallel to an optical axis of an emissionsurface of the image light in the image forming unit.
 3. The projectionoptical system according to claim 2, wherein a value obtained bydividing a focal point distance of the concave lens by a focal pointdistance of the free curved surface concave mirror is equal to orgreater than −0.6 and equal to or smaller than −0.3.
 4. The projectionoptical system according to claim 1, wherein a first interplanardistance from an emission surface of the image light in the imageforming unit to an opposing surface that opposes the image forming unitin the concave lens is shorter than a second interplanar distance fromthe opposing surface to an emission surface where the image light madeto be incident to the concave lens is emitted from the concave lens. 5.The projection optical system according to claim 1, wherein the concavelens is attached to the image forming unit through a holding member soas to oppose an emission surface of the image light in the image formingunit.
 6. A head-up display device comprising: an image forming unit thatemits image light containing image information; and an eyepiece opticalsystem that displays a virtual image by reflecting the image light;wherein the eyepiece optical system includes a concave lens, a freecurved surface lens, and a free curved surface concave mirror disposedin order from the image forming unit side along the emission directionof the image light.
 7. The head-up display device according to claim 6;wherein the image forming unit includes a backlight and a liquid crystaldisplay panel, and the concave lens is disposed so that an optical axisof the concave lens is parallel to an optical axis of an emissionsurface of the liquid crystal display panel.
 8. The head-up displaydevice according to claim 6; wherein the image forming unit includes arelay optical system that generates an image of a light valve, and ascreen plate that has a diffusion function, and the concave lens isdisposed so that an optical axis of the concave lens is disposedparallel to an optical axis of the screen plate.
 9. The head-up displaydevice according to claim 6; wherein the image forming unit includes alaser light source, a light scanning section that light-scans the laserlight source by rotation of a reflection surface, and a screen platethat has a diffusion function, and the concave lens is disposed so thatan optical axis of the concave lens is parallel to an optical axis ofthe screen plate.